The pollutant emission of an internal combustion engine can be effectively reduced by catalytic after-treatment using catalytic converters in conjunction with a lambda control device. However, an important requirement for this is that not only the lambda probe of the lambda control device but also the catalytic converter has reached its light-off temperature.
One option for rapidly heating up the catalytic converter consists in blowing secondary air into the exhaust manifold of the internal combustion engine downstream of the outlet valves. The secondary air is supplied by a secondary air pump and fed into the exhaust gas downstream of the outlet valves of the internal combustion engine via a ducting system containing a secondary air valve. The exothermic reaction of the secondary air with unburned fuel in the hot exhaust gas and its further oxidation before and in the catalytic converter results in accelerated heating of the catalytic converter to its operating temperature, thereby reducing the pollutant emissions in the warm-up phase of the internal combustion engine.
Legislative requirements provide for monitoring of the secondary air system, specifically to ensure compliance with a minimum value for the injected secondary air mass flow.
For monitoring of the secondary air mass flow, the provision of a separate air mass meter in the secondary air line is disclosed, for example, in DE 197 13 180 C1. The measurement signal of the air mass meter is recorded, the variation over time of said measurement signal is determined and a malfunction of the secondary air inflow is detected if the variation does not correspond to a predefined variation.
EP 0 928 366 B1 discloses a secondary air system for an internal combustion engine having a secondary air pipe. The air pipe is connected to an intake manifold via an inlet port and to an exhaust manifold via an outlet port. The inlet port is disposed downstream of an air flow meter measuring the air mass flowing into the cylinders of the internal combustion engine and upstream of a throttle valve. The secondary air system comprises a secondary air valve which is disposed in the secondary air pipe, and a control device with an observer which controls the opening angle of the secondary air valve. The observer, which incorporates a physical model of the intake manifold and of the secondary air system, determines an estimate of a secondary air mass flow as a function of the opening angle of the throttle valve, the engine speed and a measured value of a first air mass flow which is determined by the air mass meter.
DE 196 09 922 A1 discloses a method for monitoring secondary air injection for an internal combustion engine using a sensor for measuring the oxygen content of the exhaust gas. The method is based on the reaction of the sensor to the application of the secondary air, the amount of air sucked in by the internal combustion engine being increased when air is fed to the exhaust gas.
DE 199 52 836 C1 discloses a method for monitoring a secondary air system in combination with the exhaust system of an internal combustion engine wherein the operational efficiency of the secondary air system is assessed on the basis of a mathematically determined secondary air flow.
With the known methods, only the total secondary air mass flow fed to the exhaust gas is determined. For internal combustion engines which have different cylinder groups with separate catalytic converters, and therefore a multiflow exhaust system, such as a V-engine, for example, no distinction is made between the individual cylinder banks. Although in the event of partial line closure of or a leak in the secondary air system on one cylinder bank, this may result in an insignificant variation in the total secondary air mass flow, it can nevertheless cause a serious unequal distribution between the cylinder banks.
Future legislation prescribes that the individual cylinder banks must be monitored separately for adequate secondary air mass flow.
DE 100 65 963 A1 shows an arrangement for feeding secondary air into the exhaust gas of an internal combustion engine having various cylinder groups with separate catalytic converters. The cylinder banks of a V-engine are quoted as examples of various cylinder groups. Proposed here is cylinder-specific feeding of secondary air with at least two partly separate exhaust gas ducts using a secondary air pump, with secondary air lines which connect the outlet side of the secondary air pump to one of said separate secondary air lines. In each of the secondary air lines there is provided a separately controllable means of flow control. There is additionally provided on the outlet side of the secondary air pump another controllable port whose opening angle influences the pressure in said secondary air lines. This enables catalytic converter heating to be implemented by means of secondary air in conjunction with a rich mixture for each cylinder group independently of the other cylinder group. Secondary air system diagnostics are not discussed in this publication.